1. Field of the Invention
The present invention relates to a microwave combiner assembly, and more particularly, to a multi-element microwave combiner employing a structurally rigid assembly of elements.
2. Description of the Prior Art
The combining of negative-resistance diodes such as, for example, IMPATT diodes to amplify microwave signals generated by the diodes in oscillators and amplifiers to provide high power microwave signals has been under investigation for a number of years. Generally, a number of diodes and associated circuits are connected in parallel whereby it is intended that each of the diodes provide an equal portion of in-phase power to a load. However, since undesirable anti-phase currents may be generated as well as the desirable in-phase currents, the various configurations of combiners have incorporated numerous schemes for suppressing the anti-phase currents while providing a low impedance path for the in-phase currents. A number of techniques are described in the literature such as, for example, the publication entitled "Microwave Devices", edited by Howes and Morgan, published by John Wiley & Sons, Ltd. in 1976, and particularly Chapter 5 therein, entitled, "Micro-Wave Solid State Oscillator Circuits" by K. Kurokawa. Researchers in the past have attempted to combine as many diodes as possible in microwave oscillators and amplifiers, such as 64 diodes in a single combiner, in order to obtain the highest possible power output levels of the in-phase currents while simultaneously suppressing the anti-phase currents. The high power level combiners are achieved normally by coupling many negative-resistance diodes to a common waveguide cavity and providing the d.c. bias voltage to each of the diodes over individual bias conductors. In a paper entitled "A Multiple Diode High Average Power Avalance-Diode Oscillator" published in IEEE Trans. Microwave Theory Techniques, MTT-17, pp 1156-1158, December 1969, C. T. Rucker describes a fragile coupling capacitance and an N-way resistor network which are used to suppress unwanted currents. The coupling capacitance uses an insulating substrate which must be extremely thin to develop sufficient capacitance to couple the energy out. Furthermore, although Rucker uses a common bias conductor to provide a bias voltage simultaneously to all the diodes, the bias current must pass through the N-way resistor network which causes a loss in efficiency. Another configuration, which is described by Knerr & Murray in a paper entitled "Microwave Amplifier Using Several IMPATT Diodes in Parallel" in the 1974 IEEE International Solid State Circuits Conference Digest of Technical Papers, pp 92-93, is a multi-diode combiner which avoids passing a bias current through the resonator network but, on the other hand, requires the diodes to be mounted on gold "fuzzbuttons" which provide a relatively soft mechanical support causing a variable, non-reproducible resistance and a non-rigid structure.
The invention provides a very small microwave combiner, which can operate either as an oscillator or as a negative-resistance amplifier which is rugged in construction to withstand mechanical stresses such as vibration and shock. For some applications, such as for a small portable radar, excessive power levels are not required so that relatively few diodes would be needed for such applications, further contributing to a reduction in size.